This invention relates to cement admixtures containing an aqueous emulsion of an alkaline-curable polymr. The resulting cement mortars have excellent adhesion, flexibility, and waterproofing properties.
Aqueous emulsions of synthetic polymers have been added to cement admixtures which are used for the surface finishing of buildings or structures. The resulting cement mortars have shown improvements in adhesion, crack-resistance, impact-resistance, abrasion-resistance, flexibility, and waterproofing properties. The aqueous emulsions used have included synthetic rubber latex, acrylate emulsion, ethylene-vinyl acetate emulsion, and ethylene-vinyl chloride emulsion. Of these, the synthetic rubber latices are excellent in water- and alkali-resistance, but unsatisfactory in ozone-resistance, heat-resistance, and weather-resistance. Hence, they do not provide satisfactory cements. Ethylene-vinyl acetate emulsions provide good adhesion but are poor in water-resistance, alkali-resistance, and weather-resistance. Ethylene-vinyl chloride emulsions have good adhesion and alkali-resistance, but are poor in heat-resistance and weather-resistance. Acrylate emulsions have a good balance of properties and have been widely used to provide the best cement admixtures.
Although acrylate emulsions have been used widely, attempts have been made to improve their performance, specifically to improve the adhesion of the cement mortar. One such attempt has been the introduction of carboxyl and epoxide groups into an acrylate polymer by polymerization with ethylenically unsaturated monomers containing such groups. Another attempt has been the introduction of a cationic charge into an acrylate polymer by polymerization with an ethylenically unsaturated cationic monomer such as alkylaminoethylmethyacrylate. However, in some cases, the adhesion of the resulting cement mortar to certain adherents is still unsatisfactory, e.g., to adherents such as glazed ceramic tiles, plastic floor surfaces (epoxy resin, urethane resin, polyvinyl chloride, and the like), asphalt, concrete, steel, and plywood, as well as old and weathered concrete and mortar.
In order to increase the flexibility of the cement mortar, acrylate polymers having a low Tg are added in large amounts. The use of the low Tg polymers results in poor adhesion due to low cohesive strength. There is also a limitation on the amount of polymer emulsion which can be added to the cement. Hence, good adhesion and good flexibility have not been obtained simultaneously using the same polymer emulsion.